<template>
<ul class="list">
  <li
  class="item"
  v-for="item of letters"
  :key="item" @click="handleLtter"
  @touchstart.prevent='handleTouchStart'
  @touchmove='handleTouchMove'
  @touchend='handleTouchEnd'
  :ref="item"
  >
  {{item}}
  </li>
</ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  updata () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods: {
    handleLtter (e) {
      this.$emit('change', e.srcElement.innerText)
    },
    handleTouchStart (e) {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const touchY = (e.touches[0].clientY - 169)
          const index = Math.floor((touchY - this.startY) / 18)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 5)
      }
    },
    handleTouchEnd (e) {
      this.touchStatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
@import '~style/varibles.styl'
.list
  position absolute
  text-align center
  color $bgColor
  display flex
  flex-direction column
  justify-content center
  width .4rem
  top 1.58rem
  right 0
  bottom 0
  margin 0 .1rem
  .item
    padding .04rem 0
</style>
